Device switching speed has continued to be the operational parameter of single most importance for semiconductor devices used in communication, switching and computation applications. In order to improve device switching speed, many different physical effects have been studied. One such physical phenomenon which has led to faster semiconductor devices is that of particle tunneling through an energy barrier and, more particularly, resonant tunneling in structures having two or more energy barriers.
In resonant tunneling devices, two or more energy barrier layers surround (in two dimensions) one or more potential well layers. Resonant tunneling occurs when a charge carrier tunnels through an energy eigenstate of the potential well in response to an applied electric field. See, for example, the double barrier resonant tunneling electronic device described in Appl. Phys. Lett., 24, pp. 593-5 (1974).
Attempts at enhancing operational characteristics of double barrier resonant tunneling devices by modulation doping, creating dissimilar barrier heights, and the like have achieved some success at improving device switching speed. However, the success of these and other enhancement techniques depend almost entirely on improving carrier mobility under applied electric field conditions.